1. Field of the Invention
The present invention relates to a method for producing carbazole derivatives. Specifically, the present invention relates to a method for producing carbazole derivatives which each have a wide band gap and are good bipolar substances with a high electron-transport property and a high hole-transport property and suitable for use in light-emitting elements.
2. Description of the Related Art
A carbazole derivative represented by General Formula K1 below which covers carbazole derivatives that are desired substances of an embodiment of the present invention and a carbazole derivative represented by General Formula (1) below which is a desired substance of an embodiment of the present invention are well-known substances. It is also well known that each substance has a large band gap, can emit light of an extremely short wavelength, and can exhibit blue light emission with high color purity (see Patent Documents 1 and 2). Further, high electrochemical stability of these derivatives and also methods for producing them are naturally known (see Patent Documents 1 and 2).

As the known method for producing the derivative represented by General Formula (1), there are two methods, which are described in Patent Documents 1 and 2. The production method described in Patent Document 1 is referred to as a first known method. The first known method will be detailed hereinbelow and consists of three steps: Reaction Formulae (K-1), (K-2), and (K-3).
In accordance with the first known method, 9H-carbazole (Compound K1) is first halogenated to give a carbazole derivative (Compound K2) (Reaction Formula (K-1)). In Reaction Formula (K-1), X2 represents a halogen, preferably iodine or bromine. When bromination is carried out in Reaction Formula (K-1), examples of brominating agents that can be used include bromine, N-bromosuccinimide, and the like. Examples of solvents that can be used in this case include halogen-based solvents such as chloroform and carbon tetrachloride. When N-bromosuccinimide is used as the brominating agent, ethyl acetate, tetrahydrofuran, dimethylformamide, acetic acid, water, or the like can be used as the solvent.

When iodination is carried out in Reaction Formula (K-1), examples of iodinating agents that can be used include N-iodosuccinimide, 1,3-diiodo-5,5-dimethylimidazolidine-2,4-dione (abbreviation: DIH), 2,4,6,8-tetraiodo-2,4,6,8-tetraazabicyclo[3,3,0]octane-3,7-dione, 2-iodo-2,4,6,8-tetraazabicyclo[3,3,0]octane-3,7-dione, and the like.
Further, examples of solvents that can be used alone or in combination for iodination with such an iodinating agent include aromatic hydrocarbons such as benzene, toluene, and xylene; ethers such as 1,2-dimethoxyethane, diethyl ether, methyl-t-butyl ether, tetrahydrofuran, and dioxane; saturated hydrocarbons such as pentane, hexane, heptane, octane, and cyclohexane; halogens such as dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, and 1,1,1-trichloroethane; nitriles such as acetonitrile and benzonitrile; esters such as ethyl acetate, methyl acetate, and butyl acetate; acetic acid (glacial acetic acid); water; and the like. When water is used, water is preferably mixed with an organic solvent. Furthermore, in this reaction, acid such as sulfuric acid or acetic acid is preferably used at the same time.
Next, the carbazole derivative obtained (Compound K2) and aryl boronic acid [Compound K3 (corresponding to “Compound 3” of the present invention)] are coupled according to a Suzuki-Miyaura reaction using a palladium catalyst, whereby 3-aryl-9H-carbazole (Compound K4) is obtained (Reaction Formula (K-2)). In Reaction Formula (K-2), X2 represents a halogen, preferably iodine or bromine. Alternatively, in Reaction Formula (K-2), a compound in which X2 is a triflate group may be used. Note that an organoboron compound represented by Compound K3 is referred to as aryl boronic acid when R101 and R102 independently represent hydrogen.

In Reaction Formula (K-2), Ar1 represents an aryl group with 6 to 13 carbon atoms which may have a substituent. Examples of palladium catalysts that can be used in this reaction formula include palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), and the like. Examples of ligands of the palladium catalyst which can be used in Reaction Formula (K-2) include tri(ortho-tolyl)phosphine, triphenylphosphine, tricyclohexylphosphine, and the like.
Examples of bases that can be used in Reaction Formula (K-2) include organic bases such as sodium tert-butoxide, inorganic bases such as potassium carbonate, and the like. Examples of solvents that can be used in Reaction Formula (K-2) include a mixed solvent of toluene and water, a mixed solvent of toluene, an alcohol such as ethanol, and water, a mixed solvent of xylene and water, a mixed solvent of xylene, an alcohol such as ethanol, and water, a mixed solvent of benzene and water, a mixed solvent of benzene, an alcohol such as ethanol, and water, a mixed solvent of an ether such as ethyleneglycoldimethylether and water, and the like. Note that use of a mixed solvent of toluene and water or a mixed solvent of toluene, ethanol, and water is more preferable.
In Reaction Formula (K-3) which is the last reaction step of the first known method, an anthracene derivative (Compound K5) and the carbazole derivative (Compound K4) are coupled according to a Hartwig-Buchwald reaction using a palladium catalyst or an Ullmann reaction using copper or a copper compound. Thus, a carbazole derivative represented by General Formula (1) which is the same desired substance as a production method of an embodiment of the present invention is obtained.

In Reaction Formula (K-3), X3 represents a halogen or a triflate group; when X3 is a halogen, it is preferably iodine, bromine, or chlorine. In this reaction formula, Ar1 represents an aryl group with 6 to 13 carbon atoms which may have a substituent. Examples of palladium catalysts that can be used for a Hartwig-Buchwald reaction in Reaction Formula (K-3) include bis(dibenzylideneacetone)palladium(0), palladium(II) acetate, and the like.
Examples of ligands of the palladium catalyst which can be used in Reaction Formula (K-3) include tri(tert-butyl)phosphine, tri(n-hexyl)phosphine, tricyclohexylphosphine, and the like. Examples of bases that can be used include organic bases such as sodium tert-butoxide, inorganic bases such as potassium carbonate, and the like. Further, examples of solvents that can be used include toluene, xylene, benzene, tetrahydrofuran, and the like.
In Reaction Formula (K-3), an Ullmann reaction can be carried out instead of a Hartwig-Buchwald reaction, as described above, in which case copper or a copper compound is used instead of a palladium catalyst. In this case, R111 and R112 independently represent a halogen, an acetyl group, or the like; as the halogen, there are chlorine, bromine, and iodine. Further, use of copper(I) iodide in which R111 is iodine or copper(II) acetate in which R112 is an acetyl group is preferable. As the base that can be used in this case, an inorganic base such as potassium carbonate is given.
Further, examples of solvents that can be used in the above reaction include 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)pyrimidinone (DMPU), toluene, xylene, benzene, and the like. In an Ullmann reaction, since a reaction temperature of 100° C. or more enables the desired substance in a shorter time and a higher yield, DMPU or xylene, which has a high boiling point, is preferably used. In addition, since the reaction temperature is more preferably 150° C. or more, use of DMPU is preferred.
The first known method is as described above. A second known method is a production method described in Patent Document 2 and consists of three steps: Reaction Formulae (K-4), (K-5), and (K-6), as specifically described hereinbelow. Note that since Compound K4 which is a starting material in Reaction Formula (K-4) is obtained through two reaction steps: Reaction Formulae (K-1) and (K-2), the second known method includes another two reaction steps in a strict sense.

The carbazole derivative synthesized by the first known method (Compound K4) and para-dihalogenated benzene (Compound K6) are coupled according to a Hartwig-Buchwald reaction using a palladium catalyst or an Ullmann reaction using copper or a copper compound, whereby a carbazole derivative (Compound K7) can be obtained (Reaction Formula (K-4)). In Reaction Formula (K-4), X4 and X5 independently represent a halogen or a triflate group; when X4 and X5 independently represent a halogen, it is preferably iodine, bromine, or chlorine. In addition, X4 and X5 may be the same or different from each other. In Reaction Formula (K-4), Ar1 represents an aryl group with 6 to 13 carbon atoms which may have a substituent.
For a Hartwig-Buchwald reaction in Reaction Formula (K-4), examples of palladium catalysts that can be used include bis(dibenzylideneacetone)palladium(0), palladium(II) acetate, and the like. Examples of ligands of the palladium catalyst which can be used include tri(tert-butyl)phosphine, tri(n-hexyl)phosphine, tricyclohexylphosphine, and the like. Examples of bases that can be used include organic bases such as sodium tert-butoxide, inorganic bases such as potassium carbonate, and the like. Further, examples of solvents that can be used include toluene, xylene, benzene, tetrahydrofuran, and the like.
In Reaction Formula (K-4), an Ullmann reaction can be performed instead of a Hartwig-Buchwald reaction, as described above, in which case copper or a copper compound is used instead of a palladium catalyst. In this case, R111 and R112 independently represent a halogen, an acetyl group, or the like; as the halogen, there are chlorine, bromine, or iodine. Further, use of copper(I) iodide in which R111 is iodine or copper(II) acetate in which R112 is an acetyl group is preferable. Instead of a copper compound, copper can alternatively be used.
Furthermore, as a base that can be used in the above reaction formula, an inorganic base such as potassium carbonate is given. Examples of solvents that can be used include 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)pyrimidinone (DMPU), toluene, xylene, benzene, and the like. In an Ullmann reaction, since a reaction temperature of 100° C. or more enables the desired substance in a shorter time and a higher yield, DMPU or xylene, which has a high boiling point, is preferably used. In addition, since the reaction temperature is more preferably 150° C. or more, use of DMPU is preferred.
Next, the carbazole derivative obtained (Compound K7) undergoes boron oxidation using an alkyl lithium reagent and a boron reagent, whereby a boronic acid body (Compound K8) of the carbazole derivative is obtained (Reaction Formula (K-5)). In Reaction Formula (K-5), X5 represents a halogen or a triflate group; as the halogen, it is preferably iodine, bromine, or chlorine, and Ar1 represents an aryl group with 6 to 13 carbon atoms which may have a substituent. Further, the boronic acid of Compound K8 may be used in the subsequent reaction after being protected with ethylene glycol or pinacol.

In Reaction Formula (K-5), R50 represents an alkyl group with 1 to 6 carbon atoms, and R51 represents an alkyl group with 1 to 6 carbon atoms. Examples of solvents that can be used include ether-based solvents such as diethyl ether, tetrahydrofuran (THF), and cyclopentyl methyl ether. Further, examples of alkyl lithium reagents include n-butyllithium in which R50 is an n-butyl group, t-butyllithium in which R50 is a t-butyl group, and methyllithium in which R50 is a methyl group, and the like. Furthermore, examples of boron reagents include trimethyl borate in which R51 is a methyl group, triisopropyl borate in which R51 is an isopropyl group, and the like.
Lastly, the boronic acid body (Compound K8) of the carbazole derivative and an anthracene derivative (Compound K9) are coupled according to a Suzuki-Miyaura coupling reaction using a palladium catalyst, whereby the desired substance represented by General Formula (1) is obtained (Reaction Formula (K-6)). In Reaction Formula (K-6), X6 represents a halogen or a triflate group; when X6 is a halogen, it is preferably iodine, bromine, or chlorine.

In Reaction Formula (K-6), Ar1 represents an aryl group with 6 to 13 carbon atoms which may have a substituent. Examples of palladium catalysts that can be used include palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), and the like. Examples of ligands of the palladium catalyst which can be used in this case include tri(ortho-tolyl)phosphine, triphenylphosphine, tricyclohexylphosphine, and the like. Examples of bases that can be used in this reaction formula include organic bases such as sodium tert-butoxide, inorganic bases such as potassium carbonate, and the like
Further, examples of solvents that can be used in the above reaction include a mixed solvent of toluene and water, a mixed solvent of toluene, an alcohol such as ethanol, and water, a mixed solvent of xylene and water, a mixed solvent of xylene, an alcohol such as ethanol, and water, a mixed solvent of benzene and water, a mixed solvent of benzene, an alcohol such as ethanol, and water, a mixed solvent of an ether such as ethyleneglycoldimethylether and water, and the like. Further, use of a mixed solvent of toluene and water or a mixed solvent of toluene, ethanol, and water is more preferable. Note that instead of Compound K8, an organoboron compound obtained by protecting the boronic acid of Compound K8 with ethylene glycol or pinacol may be used.
As described above, a compound represented by General Formula (1) which is a desired substance of a production method of the present invention is a known substance, and the two methods for producing the compound is also known. Further, the compound represented by General Formula (1) has a structure in which an anthracene skeleton and a carbazole skeleton are bonded and an aryl group is bonded to the 3-position of the carbazole skeleton.
In each known production method, the formation processes is not simple due to a number of reaction steps up to formation of a desired substance. Further, any of a variety of aryl groups can be applied to an aryl group (Ar1) in a derivative represented by General Formula (1) which is a desired substance of both a production method of the present invention and the known production methods, and a wide variety of carbazole derivatives can be produced by these methods. However, since the known production methods involve, before an anthracene skeleton and a carbazole skeleton are bonded, the introduction of the aryl group that is to be bonded to the 3-position of the carbazole skeleton, it can be said that such methods are not effective in producing a wide variety of carbazole derivatives.
In other words, in the known production methods, because of the introduction of an aryl group to the 3-position of the carbazole skeleton before the anthracene skeleton and the carbazole skeleton are bonded, the bonding reaction of the both skeletons occurs after the introduction. Accordingly, in the first known method, there is a problem in that what kind of aryl group is introduced affects the reaction in which the aryl group is introduced and the following reaction in which the both skeletons are bonded, so that the yield, purity, etc. of a desired substance varies depending on the aryl group introduced.
Moreover, in the second known method, since Compound K4 which is the starting material in Reaction Formula (K-4) which is the first step is carbazole in which an aryl group is introduced, the carbazole undergoes three steps of reactions: Reaction Formulae (K-4), (K-5), and (K-6). Therefore, in each step, the aryl group substituted affects progression of the reaction. Accordingly, the yield, purity, etc. of a desired substance varies depending on the aryl group introduced to the starting material.